1. Field of Invention
This invention relates to systems and methods for print head defect detection and print head maintenance.
2. Description of Related Art
There exists printers wherein an inkjet print head moves relative to and ejects marking material toward an intermediate substrate in order to form an image on the intermediate substrate. Subsequently, the image is transferred from the intermediate substrate onto a sheet of media. The quality of the image formed on the sheet of media is influenced by, among other things, the positioning of the inkjets within the inkjet print head and the ability for the inkjets to consistently eject ink.
For example, inkjets within the inkjet print head can become clogged. The inkjets can also become misaligned such that ink is not consistently ejected in the same direction. Solid inkjet print heads are prone to randomly develop defects such as clogged or misaligned jets. Once an inkjet becomes defective, it will remain defective until the defects are corrected. In other words, the defects that exist in the inkjets and inkjet print heads are semi-stable because they do not self correct over time. Typically, some maintenance is required in order to correct the inkjets and/or inkjet print heads. The defect will thus remain with the inkjet head until some maintenance is performed. The maintenance may include a purging operation or a realignment of the inkjet heads.
Conventionally, in order to determine whether one or more inkjets is defective, an image is printed on a sheet of media and the image is visually inspected in order to detect defects in the inkjets and/or print heads. If the image contained defects, a user could then initiate print head maintenance. However, printing a separate test image and manually initiating maintenance is both system resource (e.g., media, ink, and time that might otherwise be used for productive output) and user resource (e.g., time required to initiate test image, review test image, and initiate maintenance) intensive.
Xerographic devices have addressed the problem of wasted system and user resources by printing test images onto a photoconductive (intermediate) substrate within inter-document zones. When images are laid down on the photoconductive substrate in xerographic devices, based on the typical system architecture, there is sufficient space between those images on the photoconductive substrate to print a test image between the images to be printed. By using an internal image sensor, the xerographic device can evaluate the test image for defects or unintended variations and then perform maintenance on the appropriate subsystem.